While the number of fungal species described is approximately 64,000, it is estimated that over one million species exist making this a diverse group of organisms. About 90% of fungi grow in the form of a radiating system of branching hyphae known as the mycelium. This mode of growth reflects a different life style from unitary organisms such as yeasts, with distinct advantages for advancing over surfaces and penetrating substrata (Carlile, 1994, The Growing Fungus, ed. Gow, N. A. R. & Gadd, G. M., Chapman & Hall, pp. 3–19). To date very few genes have been characterized which effect fungal branching. The most characterized gene is cot1 isolated from the fungus Neurospora crassa. Cot-1 is a temperature sensitive mutation leading to hyperbranching and the sequence, whose function is unknown, appears to encode a cAMP dependent protein kinase (Yarden et al, 1992, EMBO J. 11:2159–2166).
Filamentous fungi find industrial importance as producers of antibiotics, enzymes, fine chemicals and food (Aspergillus: 50 Years On (1994) vol 29, ed S. D. Martinelli & J. R. Kinghorn pp. 561–596). There remains a need in the art for improved methods of producing proteins in filamentous fungus. Filamentous fungus are also known pathogens of plants and animals. Therefore, understanding the genetic basis of fungal growth will provide insight regarding possible anti-fungal therapies.